Light emitting diode package and method for fabricating same

ABSTRACT

An LED package comprising a submount having a top and bottom surface with a plurality of top electrically and thermally conductive elements on its top surface. An LED is included on one of the top elements such that an electrical signal applied to the top elements causes the LED to emit light. The electrically conductive elements also spread heat from the LED across the majority of the submount top surface. A bottom thermally conductive element is included on the bottom surface of said submount and spreads heat from the submount, and a lens is formed directly over the LED. A method for fabricating LED packages comprising providing a submount panel sized to be separated into a plurality of LED package submounts. Top conductive elements are formed on one surface of the submount panel for a plurality of LED packages, and LEDs are attached to the top elements. Lenses are molded over the LEDs and the substrate panel is singulated to separate it into a plurality of LED packages.

This application is a continuation of U.S. patent application Ser. No.14/705,228, filed on May 6, 2015, which is a divisional of, and claimsthe benefit of, U.S. patent application Ser. No. 11/982,275 to Keller etal., filed on Oct. 31, 2007.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to light emitting diodes, and in particular tolight emitting diode packages having a molded lens.

Description of the Related Art

Light emitting diodes (LED or LEDs) are solid state devices that convertelectric energy to light, and generally comprise one or more activelayers of semiconductor material sandwiched between oppositely dopedlayers. When a bias is applied across the doped layers, holes andelectrons are injected into the active layer where they recombine togenerate light. Light is emitted from the active layer and from allsurfaces of the LED.

In order to use an LED chip in a circuit or other like arrangement, itis known to enclose an LED chip in a package to provide environmentaland/or mechanical protection, color selection, focusing and the like. AnLED package also includes electrical leads, contacts or traces forelectrically connecting the LED package to an external circuit. In atypical LED package 10 illustrated in FIG. 1A, an LED chip 12 is mountedon a reflective cup 13 by means of a solder bond or conductive epoxy.One or more wire bonds 11 connect the ohmic contacts of the LED chip 12to leads 15A and/or 15B, which may be attached to or integral with thereflective cup 13. The reflective cup may be filled with an encapsulantmaterial 16 containing a wavelength conversion material such as aphosphor. Light emitted by the LED at a first wavelength may be absorbedby the phosphor, which may responsively emit light at a secondwavelength. The entire assembly is then encapsulated in a clearprotective resin 14, which may be molded in the shape of a lens tocollimate the light emitted from the LED chip 12. While the reflectivecup 13 may direct light in an upward direction, optical losses may occurwhen the light is reflected (i.e. some light may be absorbed by thereflector cup instead of being reflected). In addition, heat retentionmay be an issue for a package such as the package 10 shown in FIG. 1A,since it may be difficult to extract heat through the leads 15A, 15B.

A conventional LED package 20 illustrated in FIG. 1B may be more suitedfor high power operations which may generate more heat. In the LEDpackage 20, one or more LED chips 22 are mounted onto a carrier such asa printed circuit board (PCB) carrier, substrate or submount 23. A metalreflector 24 mounted on the submount 23 surrounds the LED chip(s) 22 andreflects light emitted by the LED chips 22 away from the package 20. Thereflector 24 also provides mechanical protection to the LED chips 22.One or more wirebond connections 11 are made between ohmic contacts onthe LED chips 22 and electrical traces 25A, 25B on the carrier 23. Themounted LED chips 22 are then covered with an encapsulant 26, which mayprovide environmental and mechanical protection to the chips while alsoacting as a lens. The metal reflector 24 is typically attached to thecarrier by means of a solder or epoxy bond.

While a package such as the package 20 illustrated in FIG. 1B may havecertain advantages for high power operation, there may be a number ofpotential problems associated with using a separate metal piece as ametal reflector. For example, small metal parts may be difficult tomanufacture repeatable with a high degree of precision at a reasonableexpense. In addition, since the reflector is typically affixed to acarrier using an adhesive, several manufacturing steps may be requiredto carefully align and mount the reflector, which may add to the expenseand complexity of the manufacturing process for such packages.

For higher powered operation it may also be difficult to transferdissipate heat generated by the LED chip 22. Submounts can be made ofmaterials such as ceramics that are robust but do not efficientlyconduct heat. Heat from the LED chip passes into the submount below theLED chip, but does not efficiently spread outward from below the LEDwhere it can then dissipate. Heat from the LED tends to localize belowthe LED and can increase as operation of the LED package. This increasedheat can result is reduced lifetime or failure of the package.

SUMMARY OF THE INVENTION

One embodiment of an LED package according to the present inventioncomprises a submount having a top and bottom surface with a plurality oftop electrically and thermally conductive elements on its top surface.An LED is included on one of the top elements such that an electricalsignal applied to the top elements causes the LED to emit light. Theelectrically conductive elements also spread heat from the LED acrossthe majority of the submount top surface. A bottom thermally conductiveelement is included on the bottom surface of said submount and conductsheat from the submount. A lens is formed directly over the LED.

Another embodiment of an LED package according to the present inventioncomprises a submount having a top and bottom surface with an attach padon the top surface, a first contact pad on the top surface is integralto the attach pad, and a second contact pad on the top surface. An LEDis mounted to the attach pad, and when an electrical signal is appliedto the first and second contact pads causing the LED to emit light. Thepads also comprise thermally conductive layers covering most of the topsurface to spread heat from the LED to the majority of the top surface.An optical element is formed directly over said LED.

Another embodiment of an LED package according to the present inventioncomprises, a submount having a top and bottom surface, with an LEDmounted on the top surface. A lens is formed directly on the LED and aportion of the top surface. A top heat spreading element on the topsurface spreads heat from the LED across the majority of the topsurface, and a bottom heat spreading element on the bottom surface ofthe submount that conducts heat from the submount.

One embodiment of a method for fabricating LED packages according to thepresent invention, comprises providing a submount panel sized to beseparated into a plurality of LED package submounts. Top conductiveelements are formed on one surface of the submount panel for a pluralityof LED packages. LEDs are attached to the top elements with the LEDselectrically connected to the top conductive elements. Lenses are moldedover the LEDs and the substrate panel is singulated to separate it intoa plurality of LED packages.

A method for fabricating a plurality of surface mount LED packagesaccording to the present invention, comprises providing a submount panelsized to accommodate formation of a plurality of LED packages. Sets ofattach pads and contact pads are formed on one surface of the submountpanel, with each of the sets corresponding to one of the LED packages tobe formed from said submount panel. A plurality of LEDs are attached tothe submount panel with each of the LEDs attached and electricallyconnected to one of the sets of attach pads and contact pads. Aplurality of lenses are molded on the submount panel with each of thelenses over one of the LEDs. Sets of surface mount contacts are formedon the surface of the submount panel opposite the sets of attach padsand contact pads, each of the sets of surface mount contactscorresponding to a respective one of the sets of attach pads and contactpads. The substrate panel is singulated to separate it into a pluralityof LED packages.

These and other aspects and advantages of the invention will becomeapparent from the following detailed description and the accompanyingdrawings which illustrate by way of example the features of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a sectional view of a prior art LED package;

FIG. 1B is a sectional view of another prior art LED package;

FIG. 2a is a top view of one embodiment of an LED package according tothe present invention;

FIG. 2b is a side view of the LED package shown in FIG. 2 a;

FIG. 2c is a bottom view of the LED package shown in FIG. 2 a;

FIG. 2d is an upper perspective view of the LED package shown in FIG. 2a;

FIG. 2e is a bottom perspective view of the LED package shown in FIG. 2a;

FIG. 2f is an exploded view of the LED package shown in FIG. 2 a;

FIG. 2g is a sectional view of the LED package shown in FIG. 2a , takenalong section lines 2 g-2 g;

FIG. 3a is a side view of another embodiment of an LED package accordingto the present invention;

FIG. 3b is top view of the LED package shown in FIG. 3 a;

FIG. 3c is a bottom view of the LED package shown in FIG. 3 a;

FIG. 3d is an upper perspective view of the LED package shown in FIG. 3a;

FIG. 3e is a bottom perspective view of the LED package shown in FIG. 3a;

FIG. 4a is an upper perspective view of another embodiment of an LEDpackage according to the present invention;

FIG. 4b is a bottom perspective view of the LED package shown in FIG. 2a;

FIG. 5 is a flow diagram for one embodiment of a fabrication methodaccording to the present invention;

FIG. 6a is a sectional view of one embodiment of a lens mold accordingto the present invention;

FIG. 6b is another sectional view of the lens mold shown in FIG. 5 a;

FIG. 7a is a plan view of one embodiment of a submount panel with lensesarranged according to the present invention; and

FIG. 7b is a sectional view of the submount panel taken in FIG. 7a takenalong section lines 7 b-7 b.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to compact, simple and efficient LEDpackages and methods for manufacturing same. Different embodiments cancomprise one or more high power LEDs that typically operate at elevatedtemperatures. Packages according to the present invention can includefeatures to provide for improved thermal management by spreading theheat from the LED. The heat can then dissipate into the ambient. Thepackages according to the present invention can also comprise a lensmolded directly over the one or more LEDs to protect the LED while stillallowing for efficient emission characteristics.

The present invention is also directed to methods for fabricating LEDpackages using processing steps that allow for the simultaneousformation of a plurality of packages. This can reduce the manufacturingcomplexity and cost of LED package fabrication.

The present invention provides low cost, relatively small size LEDpackages that provide an efficient but small light source. The packagesaccording to the present invention are particularly adapted to surfacemount technologies and provide features that allow for the good thermaldissipation, allowing the packages to operate at elevated power levelswithout overheating.

It is understood that when an element such as a layer, region orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. Furthermore, relative terms such as “inner”, “outer”, “upper”,“above”, “lower”, “beneath”, and “below”, and similar terms, may be usedherein to describe a relationship of one layer or another region. It isunderstood that these terms are intended to encompass differentorientations of the device in addition to the orientation depicted inthe figures.

Although the terms first, second, etc. may be used herein to describevarious elements, components, regions, layers and/or sections, theseelements, components, regions, layers and/or sections should not belimited by these terms. These terms are only used to distinguish oneelement, component, region, layer or section from another region, layeror section. Thus, a first element, component, region, layer or sectiondiscussed below could be termed a second element, component, region,layer or section without departing from the teachings of the presentinvention.

Embodiments of the invention are described herein with reference tocross-sectional view illustrations that are schematic illustrations ofidealized embodiments of the invention. As such, variations from theshapes of the illustrations as a result, for example, of manufacturingtechniques and/or tolerances are expected. Embodiments of the inventionshould not be construed as limited to the particular shapes of theregions illustrated herein but are to include deviations in shapes thatresult, for example, from manufacturing. A region illustrated ordescribed as square or rectangular will typically have rounded or curvedfeatures due to normal manufacturing tolerances. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region of a device andare not intended to limit the scope of the invention.

The present invention can be used in with many different solid stateemitters with the embodiments of the invention below being described inrelation to LEDs, and in particular to white emitting LEDs and LEDpackages. It is understood that the present invention can also use othersolid state emitter packages beyond the embodiment shown. The presentinvention can also be used with multiple emitter packages, such as LEDpackages having more than one LED. The present invention can be used inany application wherein a conversion material is used to down-convertthe wavelength of light from an emitter, and the discussion of thepresent invention with reference to the following embodiment should notbe construed as limiting to the that particular embodiment or similarembodiments.

FIGS. 2a through 2g show one embodiment of an LED package 30 accordingto the present invention generally comprising a substrate/submount(“submount”) 32 with one or more LEDs emitting the same or differentcolors. In the embodiment shown, a single LED 34 is mounted on thesubmount 32. The LED 34 can have many different semiconductor layersarranged in different ways. LED structures and their fabrication andoperation are generally known in the art and only briefly discussedherein. The layers of the LED 34 can be fabricated using known processeswith a suitable process being fabrication using metal organic chemicalvapor deposition (MOCVD). The layers of the LEDs 34 generally comprisean active layer/region sandwiched between first and second oppositelydoped epitaxial layers all of which are formed successively on a growthsubstrate. LEDs can be formed on a wafer and then singulated formounting in a package. It is understood that the growth substrate canremain as part of the final singulated LED or the growth substrate canbe fully or partially removed.

It is also understood that additional layers and elements can also beincluded in the LED 34, including but not limited to buffer, nucleation,contact and current spreading layers as well as light extraction layersand elements. The active region can comprise single quantum well (SQW),multiple quantum well (MQW), double heterostructure or super latticestructures. The active region and doped layers may be fabricated fromdifferent material systems, with preferred material systems beingGroup-III nitride based material systems. Group-III nitrides refer tothose semiconductor compounds formed between nitrogen and the elementsin the Group III of the periodic table, usually aluminum (Al), gallium(Ga), and indium (In). The term also refers to ternary and quaternarycompounds such as aluminum gallium nitride (AlGaN) and aluminum indiumgallium nitride (AlInGaN). In a preferred embodiment, the doped layersare gallium nitride (GaN) and the active region is InGaN. In alternativeembodiments the doped layers may be AlGaN, aluminum gallium arsenide(AlGaAs) or aluminum gallium indium arsenide phosphide (AlGaInAsP).

The growth substrate can be made of many materials such at sapphire,silicon carbide, aluminum nitride (AlN), GaN, with a suitable substratebeing a 4H polytype of silicon carbide, although other silicon carbidepolytypes can also be used including 3C, 6H and 15R polytypes. Siliconcarbide has certain advantages, such as a closer crystal lattice matchto Group III nitrides than sapphire and results in Group III nitridefilms of higher quality. Silicon carbide also has a very high thermalconductivity so that the total output power of Group-III nitride deviceson silicon carbide are typically not limited by the thermal dissipationof the substrate (as may be the case with some devices formed onsapphire). SiC substrates are available from Cree Research, Inc., ofDurham, N.C. and methods for producing them are set forth in thescientific literature as well as in a U.S. Pat. No. Re. 34,861; U.S.Pat. Nos. 4,946,547; and 5,200,022.

The LED 34 can also comprise a conductive current spreading structure 36and wire bond pads 38 on its top surface, both of which are made of aconductive material and can be deposited using known methods. Somematerials that can be used for these elements include Au, Cu, Ni, In,Al, Ag or combinations thereof and conducting oxides and transparentconducting oxides. The current spreading structure 36 generallycomprises conductive fingers 37 arranged in a grid on the LED 34 withthe fingers spaced to enhance current spreading from the pads 38 intothe LED's top surface. In operation, an electrical signal is applied tothe pads 38, such as through a wire bond as described below, and theelectrical signal spreads through the fingers 37 of the currentspreading structure 36 and the top surface into the LED 34. Currentspreading structures are often used in LEDs where the top surface isp-type, but can also be used for n-type materials.

The LED can be coated with one or more phosphors with the phosphorsabsorbing at least some of the LED light and emitting a differentwavelength of light such that the LED emits a combination of light fromthe LED and the phosphor. In a preferred embodiment the LED emits awhite light combination of LED and phosphor light. The LED can be coatedand fabricated using many different methods, with one suitable methodbeing described in U.S. patent application Ser. No. 11/656,759 and Ser.No. 11/899,790, both entitled “Wafer Level Phosphor Coating Method andDevices Fabricated Utilizing Method”, and both of which are incorporatedherein by reference. Alternatively the LEDs can be coated using othermethods such an electrophoretic deposition (EPD), with a suitable EPDmethod described in U.S. patent application Ser. No. 11/473,089 entitled“Close Loop Electrophoretic Deposition of Semiconductor Devices”, whichis also incorporated herein by reference. It is understood that LEDpackages according to the present invention can also have multiple LEDsof different colors, one or more of which may be white emitting.

The submount 32 can be formed of many different materials with apreferred material being electrically insulating. Suitable materialsinclude, but are not limited to ceramic materials such as aluminumoxide, aluminum nitride or organic insulators like polyimide(PI) andpolyphthalamide(PPA). In other embodiments the submount 32 can comprisea printed circuit board (PCB), sapphire or silicon or any other suitablematerial, such as T-Clad thermal clad insulated substrate material,available from The Bergquist Company of Chanhassen, Minn. For PCBembodiments different PCB types can be used such as standard FR-4 PCB,metal core PCB, or any other type of printed circuit board. As morefully described below, LED packages according to the present inventioncan be fabricated using a method that utilizes a submount panel sized toaccommodate a plurality of sumbmounts. Multiple LED packages can beformed on the panel, with the individual packages being singulated fromthe panel.

The submount 32 has a top surface 40 comprising patterned conductivefeatures that can include a die attach pad 42 with an integral firstcontact pad 44. A second contact pad 46 is also included on thesubmount's top surface 40 with the LED 34 mounted approximately at thecenter of the attach pad 42. These patterned conductive features provideconductive paths for electrical connection to the LED 34 using knowncontacting methods. The LED can be mounted to the attach pad 42 usingknown methods and material mounting such as using conventional soldermaterials that may or may not contain a flux material or dispensedpolymeric materials that may be thermally and electrically conductive.

The size of the submount 32 in package 30 can vary depending ondifferent factors, with one being the size of the LED. For example, thesize of the package 30 can be essentially of the same dimension as theeffective heat spreading area in the attach pad, and first and secondcontact pads 42, 44, and 46. In a package having a 1 mm LED, thesubmount can be approximately 3.5 mm by 3.5 mm; with a package having a0.7 mm chip it can be 3.2 mm by 3.2 mm and generally of square shape inboth cases. It is further understood that the submount can have othershapes including circular, rectangular or other multiple sided shapes.

The attach pad 42 and first and second contact pads 44, 46 can comprisemuch different material such as metals or other conductive materials. Inone embodiment the pads 42, 44, 46 comprise copper deposited using knowntechniques such as plating. In typical plating process a titaniumadhesion layer and copper seed layer are sequentially sputtered onto asubstrate. Then, approximately 75 microns of copper is plated onto thecopper seed layer. The resulting copper layer being deposited can thenbe patterned using standard lithographic processes. In other embodimentsthe layer can be sputtered using a mask to form the desired pattern.

In some embodiments according to the present invention some of theconductive features can include only copper, with others of the featuresincluding additional materials. For example, the attach pad 42 can beplated or coated with additional metals or materials to the make theattach pad 42 more suitable for mounting an LED 34. For example, theattach pad 42 can be plated with adhesive or bonding materials, orreflective and barrier layers.

A gap 48 (best shown in FIGS. 2a and 2d ) is included between the secondpad 46 and the attach pad 42 down to the surface of the submount 32that, with the gap providing electrical isolation between the attach pad42 and second pad 46. As more further described below, an electricalsignal is applied to the LED 34 through the second pad 46 and the firstpad 44, with the electrical signal on the first pad 44 passing directlyto the LED 34 through the attach pad 42 and the signal from the secondpad passing into the LED 34 through wire bonds. The gap 48 provideselectrical isolation between the second pad and attach pad to preventshorting of the signal applied to the LED 34.

In some embodiments an electrical signal can be applied to the package30 by providing external electrical contact to the first and second bondpads 44, 46 such as by solder contacts or other conductive paths to aPCB. In the embodiment shown the LED package 30 is arranged for mountingusing surface mount technology and having internal conductive paths. TheLED 30 comprises first and second surface mount pads 50, 52 (best shownin FIGS. 2c and 2e ) that can be formed on the submount's back surface54, at least partially in alignment with the first and second contactpads 44, 46, respectfully. Conductive vias 56 are formed through thesubmount 32 between the first mounting pad 50 and the first contact pad44, such that when a signal is applied to the first mounting pad 50 isconducted to first contact pad 44. Similarly, conductive vias 56 areformed between the second mounting pad 52 and second contact pad 46 toconduct an electrical signal between the two. The first and secondmounting pads 50, 52 allow for surface mounting of the LED package 30with the electrical signal to be applied to the LED 34 applied acrossthe first and second mounting pads 50, 52. The vias 56 and mounting pads50,52 can made of many different materials deposited using differenttechniques, such as those used for the attach and contact pads 42, 44,46.

It is understood that the mounting pads 50, 52 and vias 56 can bearranged in many different ways and can have many different shapes andsizes. It is also understood that instead of vias, one or moreconductive traces can be provided on the surface of the submount betweenthe mounting pads and contact pads, such as along the side surface ofthe submount.

A solder mask 58 made of conventional materials can be included on thesubmount's top surface 40, at least partially covering the attach pad 42and the first and second contact pads 44, 46, and at least partiallycovering the gap 48. The solder mask 58 protects these features duringsubsequent processing steps and in particular mounting the LED 34 to theattach pad 42 and wire bonding. During these steps there can be a dangerof solder or other materials depositing in undesired areas, which canresult in damage to the areas or result in electrical shorting. Thesolder mask serves as an insulating and protective material that canreduce or prevent these dangers. The solder mask comprises an openingfor mounting the LED 34 to the attach pad 42 and for attaching wirebonds to the second contact pad 46. It also comprises side openings 60to allow convenient electrical access to the contact pads 44, 46 fortesting the package 30 during fabrication. The solder mask 58 also hasalignment holes that provide for alignment during fabrication of thepackage 30 and also allow for alignment when mounted in place by the enduser.

In some embodiments the solder mask can be provided with a symbol orindicator 69 to illustrate which side of the LED package 30 should becoupled to the plus or minus of the signal to be applied to the package.This can ensure accurate mounting of the LED package 30 to a PCB orother fixture, whether by machine or hand. In the embodiment shown thesymbol 69 comprises a plus (+) sign over the first contact pad 44,indicating that the package 30 should be mounted with the positive ofthe signal coupled to the first mounting pad 50. The minus of the signalwould then be coupled to the second mounting pad 52. It is understoodthat many different symbol types can be used and that a symbol can alsobe included over the second conductive pad 46. It is also understoodthat the symbols can be placed in other locations other than the soldermask 58.

The package 30 can also comprise elements to protect against damage fromelectrostatic discharge (ESD). In the embodiment shown the elements areon-chip, and different elements can be used such as various verticalsilicon (Si) Zener diodes, different LEDs arranged in parallel andreverse biased to the LED 34, surface mount varistors and lateral Sidiodes. In the embodiment shown a Zener diode 62 is utilized and ismounted to the attach pad 42 using known mounting techniques. The diodeis relatively small so that it does not cover an excessive area on thesurface of the submount 32.

It is noted that the solder mask 58 includes and opening for the ESDdiode 62 so that it can be mounted to the attach pad 42. Differentmounting materials and methods can be used such as those used to mountthe LED 34 to the attach pad 42. An ESD wire bond 64 is included betweenthe second contact pad 46 at the solder mask opening and the ESD diode62. Two LED wire bonds 65 are also included between the solder maskopening in the second contact pad 46 and wire bond pads 38 on the LED34. In other embodiments only one wire bond can be included between theLED 34 and second contact pad. This LED 34 and ESD diode 62 arrangementallows excessive voltage and/or current passing through the LED package30 from an ESD event to pass through the diode 62 instead of the LED 34,protecting the LED 34 from damage. The wire bonds 64 and 65 can beapplied using known methods and can comprise known conductive materials,with a suitable material being gold (Au). It is understood that in otherembodiments of an LED package according to the present invention can beprovided without an ESD element/diode or with an ESD element/diode thatis external to the LED package 30.

As mentioned above, heat typically does not spread efficiently into thesubmount 32, particularly those made of materials such as ceramic. Whenan LED is provided on an attach pad that extends generally only underthe LED, heat does not spread through most of the submount, and isgenerally concentrated to the area just below the LED. This can causeoverheating of the LED which can limit the operating power level for theLED package.

To improve heat dissipation in the LED package 30 the pads 42, 44, 46provide extending thermally conductive paths to laterally conduct heataway from the LED 34 such that it can spread to other areas of thesubmount beyond the areas just below the LED 34. The attach pad 42covers more of the surface of the submount 32 than the LED 34, with theattach pad extending from the edges of the LED 34 toward the edges ofthe submount 32. In the embodiment shown, the attach pad 42 is generallycircular and extending radially from LED 34 toward the edges of thesubmount 32. A portion of the attach pad 42 intersects with the firstand second contact pads 44, 46, with the gap 48 separating part of theattach pad adjacent to the second contact pad 46. It is understood thatthe contact pad 42 can be many other shapes and in some embodiments itcan extend to the edge of the submount 32.

The contact pads 44, 46 also cover the surface of the submount 32extending out from the vias, and covering the area between the vias 56,and the area between the vias 56 and the edges of the submount 32. Byextending the pads 42, 44 and 46 this way, the heat spreading from theLED 34 is improved. This improves thermal dissipation of heat generatedin the LED 34, which improves its operating life and allows for higheroperating power. The pads 42, 44, and 46 can cover different percentagesof the top surface 40 of the submount 32, with a typical coverage areabeing greater than 50%. In the LED package 30, the pads 42, 44 and 46can cover approximately 70% of the submount. In other embodiments thecoverage area can be greater than 75%.

The LED package 30 can further comprise a metalized area 66 on the backsurface 54 of the submount, between the first and second mounting pads50, 52. The metalized area is preferably made of a heat conductivematerial and is preferably in at least partial vertical alignment withthe LED 34. In one embodiment, the metalized area is not in electricalcontact with the elements on top surface of the submount 32 or the firstand second mounting pads on the back surface of the submount 32.Although heat from the LED is laterally spread over the top surface ofthe submount by the attach pad 42 and the pads 44, 46 more heat willpass into the submount 32 directly below and around the LED 34. Themetalized area can assist with this dissipation by allowing this heat tospread into the metalized area where it can dissipate more readily. Itis also noted that the heat can conduct from the top surface of thesubmount 32, through the vias 56, where the heat can spread into thefirst and second mounting pads 50, 52 where it can also dissipate. Forthe package 30 used in surface mounting, the thickness of the metalizedarea 66 (best shown in FIGS. 2c and 2e ) and the first and second pads50, 52 should be approximately the same such that all three make contactto a lateral surface such as a PCB.

Three solder dams 67 can be included around the area of the attach pad42 for mounting of the LED 34, with the solder dams serving to helpcenter the LED and to reduce movement of the LED from the mounting areaduring while the mounting solder is in liquid form. When the liquidsolder encounters any one of the dams, movement is slowed or stopped.This helps reduce the movement of the LED until the solder hardens.

An optical element or lens 70 is formed on the top surface 40 of thesubmount 32, over the LED 34, to provide both environmental and/ormechanical protection. The lens 70 can be in different locations on thetop surface 40 with the lens located as shown with the LED 34 atapproximately the center of the lens base. In some embodiments the lenscan be formed in direct contact with the LED 34 and the submount's topsurface 40. In other embodiments there may be an intervening material orlayer between the LED 34 and/or top surface 40. Direct contact to theLED 34 provides certain advantages such as improved light extraction andease of fabricating.

As further described below, the lens 70 can be molded using differentmolding techniques and the lens can be many different shapes dependingon the desired shape of the light output. One suitable shape as shown ishemispheric, with some examples of alternative shapes being ellipsoidbullet, flat, hex-shaped and square. Many different materials can beused for the lens such as silicones, plastics, epoxies or glass, with asuitable material being compatible with molding processes. Silicone issuitable for molding and provides suitable optical transmissionproperties. It can also withstand subsequent reflow processes and doesnot significantly degrade over time. It is understood that the lens 70can also be textured to improve light extraction or can containmaterials such as phosphors or scattering particles.

The LED package 30 can also comprise a protective layer 74 covering thesubmount's top surface 40 between the lens 70 and edge of the submount32. The layer 74 provides additional protection to the elements on thetop surface to reduce damage and contamination during subsequentprocessing steps and use. Protective layer 74 can be formed duringformation of the lens 70 and can comprise the same material as the lens70. It is understood, however, that the LED package 30 can also beprovided without the protective layer 74.

The lens 70 should also be able to withstand certain sheer forces beforebeing displaced from the submount 32. In one embodiment, the lens canwithstand a 1 kilogram (kg) or more sheer force. In embodiments of theLED package using silicones that are harder after curing and have ahigher durometer reading, such as Shore A 70 or higher, tend to betterwithstand sheer forces. Properties such as high adhesion and hightensile strength may also contribute to the ability of the lens towithstand sheer forces.

The lens arrangement of the LED package 30 is also easily adapted foruse with secondary lens or optics that can be includes over the lens bythe end user to facilitate beam shaping. These secondary lenses aregenerally known in the art, with many of them being commerciallyavailable.

FIGS. 3a to 3e show another embodiment of an LED package 100 accordingto the present invention having similar features to those in LED package30. For similar features the same reference numbers are used herein andin FIGS. 4a and 4b below with the understanding that the descriptionabove applies equally to this embodiment. The LED package 100 comprisesa submount 32, and LED 34, a lens 70 and wire bonds 64 and 65. Like theLED package 30, LED package 100 is arranged for surface mounting but hasa different arrangement for its conductive pads that provides forcontacting at one side of the submount 32.

The LED package comprises an attach pad 102 with an integral firstcontact pad 104, separated by a gap 108 from a second contact pad 106. Agap 108 provides electrical isolation as described above. The LED 34 ismounted to the attach pad using the methods described above, and thewire bond 65 runs between the second contact pad 106 to conduct theelectrical signal at the second contact pad 106 to the LED 34. The firstand second contact pads 104, 106 are not on opposite sides of thesubmount 32, but are instead on the same side. The attach pad 102 coversmost of the submount's top surface 40 to provide improved heat spreadingas described above. The first and second contact pads 104, 106 alsocover portions of the top surface to assist in current spreading.

First and second surface mount contact 110, 112 are included on thesubmount's back surface 54, at least in partial vertical alignment withthe first and second contact pads 104, 106, respectively. Conductivevias 114 run through the submount between the first surface mountcontact 110 and the first contact pad 104, and the second surface mountcontact 112 and the second contact pad 106, so that an electrical signalon the surface mount contacts 110, 112 is conducted through the vias tothe contact pads 104, 106. The signal is then conducted to the LED 34.The LED package 100 also comprises a metalized area 116 to furtherimprove heat spreading from the LED 34 and submount 32. The metalizedarea 116, however, is not between the surface mount contacts 110, 112but covers an area of the back surface 54 opposite them.

The LED package 100 as shown does not have a protective layer coveringthe submount's top surface 40 between the edge of the lens 70 and theedge of the top surface 40, although such a protective layer can beincluded in other embodiments. The LED package 100 can also be providedwith an ESD protection element 62 and solder mask 58 as described above.The LED package 100 provides for improved thermal management as in LEDpackage 30, but allows for surface mount contacting along one side ofthe submount instead of opposite sides. The LED package can also includesymbols 118 to assist in alignment by the end user.

FIGS. 4a and 4b show still another embodiment of an LED package 150according to the present invention generally comprising a submount 32,LED 34, first and second contact pads 50, 52, vias 56, ESD diode 62,wire bonds 64, 65, metalized area 66, lens 70 and protective layer 74.In this embodiment, however, the attach pad is not circular, but incombination with the first contact pad, comprises a rectangular shapedfirst conductive layer 152 on and covering the majority the submount 32.Vias 56 run between the first layer 152 and the first contact pad 50 onone side of the first layer 152, with the LED and ESD diode mounted to aattach pad area on the opposing side.

A second conductive layer 154 covers most of the remainder of thesubmount's top surface, with a gap 156 between the first and secondlayers 152, 154. Vias 56 run between the second layer 154 and the secondcontact pad 52, with the wire bonds 64, 65 running between the secondlayer 154 and the LED 43 and ESD diode 62. Like the embodiments above,an electrical signal applied to the first and second contact pads 50, 52is conducted to the LED 34, causing it to emit light.

In this embodiment, the first and second layers 152, 154 coversubstantially all of the submount's top surface, providing thecapability for broad lateral heat spreading from the LED 34. Thisarrangement, however, presents a minimal pattern for pattern recognitionduring assembly. By comparison, the shaped pad arrangement shown inFIGS. 2a-2g provides for greater pattern recognition for assembly, whileat the same time providing suitable lateral current spreading.

The present invention also provides for improved methods for fabricatingLED packages wherein multiple packages can be fabricated simultaneously.This reduces cost and complexity in fabrication, and allows forfabrication of devices with controlled features and emissioncharacteristics. FIG. 5 shows one embodiment of an LED packagefabrication method 200 according to the present invention. In 202 asubstrate (submount) panel that can be diced in subsequent manufacturingsteps to provide a plurality of individual submounts. A panel isprovided to allow for the simultaneous fabrication of a plurality ofpackages. It is understood that a separate processing step is requiredfor providing the LED package conductive features on the panel. Thesefeatures can include the attach pad, contact pads, surface mount pads,vias and metalized area, all of which can be arranged to assist indissipating heat generated by the LED. The panel will comprise aplurality of these features arranged in sets, each of the setscorresponding to one of the plurality of packages to be formed from thepanel. Many different panel sizes can be used such as for example, 3inches by 4 inches, 2 inches by 4 inches, and 4 inches by 4 inches.

In 204 a plurality of LEDs are provided, each of which is to be mountedto a respective one of the attach pads on the substrate panel. In oneembodiment, the plurality of LEDs comprise white emitting LEDs chips,and many different white chips can be used with a suitable white chipbeing described in the patent applications mentioned above andincorporated herein. In other embodiments more than one LED can beprovided for mounting to each of the attach pads. In this step aplurality of ESD protection elements can also be provided, each of whichcan be mounted in conjunction with one of the attach pads to provide ESDprotection for its LED package.

In 206 each of the LEDs is die attached to the one of the attach pads,and as mentioned above, many different mounting methods and materialscan be used, with a suitable method being mounting using conventionalsolder materials and methods. In this step each of the ESD elements canalso be mounted to a respective attach pad using the same mountingmethod and material. It is understood that the ESD element can also bemounted in other locations using other methods.

In 208 the panel undergoes a solder flux clean to remove any flux thatmay have accumulated during previous processing steps. In 210 wire bondsare formed on the for each of the LEDs and ESD elements electricallyconnecting them to the appropriate one of their respective contact pads.As described above, each of the LEDs and their accompanying ESD elementcan be wire bonded to the second contact pad. The wire bonds can beformed using known processes and can be made of known conductivematerials such as gold.

In some embodiments the LEDs can be provided and mounted to the panelwithout the desired conversion material. In these embodiments theconversion material can be deposited on the LED after wire bonding. Inoptional 212 the conversion material or phosphor is deposited on the LEDand many different known phosphor deposition methods can be used such aselectophoretic deposition or EPD. Many different phosphor depositionprocesses can be used with a suitable EPD process described in thepatent application described above.

In 214 a lens is molded over each of the LEDs and many different moldingmethods can be used. In one embodiment a molding process is used thatsimultaneously forms lenses over the LEDs in the submount panel. Onesuch molding process is referred to as compression molding processes.Referring now to FIGS. 6a and 6b one embodiment of compression moldingis shown wherein a mold 250 is provided having a plurality of cavities252 each of which has an inverted shape of the lens, wherein each cavity252 is arranged to align with a respective one of the LEDs 254 on asubstrate panel 256. The mold 250 is loaded with a lens material 257 inliquid form filling the cavities 252, with the preferred material beingliquid curable silicone. Referring to 5 b, the panel 256 is moved towardthe cavity with each of the LEDs 254 being embedded in the liquidsilicone within one a respective one of the cavities 252. In oneembodiment a layer of silicone can also remain between adjacent lensesthat provides a protective layer over the top surface of the submount.The liquid silicone can then be cured using known curing processes. Thepanel can then be removed from the mold and as shown in FIGS. 7a and 7bthe panel can comprise a plurality of lenses 258, each of which is overa respective one of the LEDs 254. The individual LED packages can thenbe separated from the panel, such as along dashed lines shown.

Referring again to FIG. 5, in 216 the panel can then diced/singulated toseparate the individual LED packages and different methods can be usedsuch as known saw singulation methods. When using this method a tape canbe attached to the panel prior to singulation to hold and stabilize thepanel and individual LED packages. Following singulation, the LEDpackages can be cleaned and dried.

In 218 each of the LED packages can be tested to be sure they areoperating correctly and to measure each device output lightcharacteristics. It is understood that the packages can also be testedat different points in this method by probing the submount panel. In 220the LED packages can be binned according to their outputcharacteristics, packaged according to each bin, and shipped to thecustomer.

One embodiment of a method is described herein, but it is understoodthat different embodiments of methods according to the present inventioncan use the same steps in different order or can have different steps.Regarding the LED packages, the present invention has been described indetail with reference to certain preferred configurations thereof, otherversions are possible. Therefore, the spirit and scope of the inventionshould not be limited to the versions described above.

We claim:
 1. A light emitting diode (LED) package, comprising: asubmount comprising a first side and a second side that is opposite thefirst side; a first contact pad and a second contact pad on the firstside of the submount; an LED mounted on at least one of the firstcontact pad and the second contact pad; and a solder mask on the firstcontact pad and the second contact pad, wherein a portion of the soldermask forms at least one symbol that indicates a mounting orientation theLED package.
 2. The LED package of claim 1, wherein the mountingorientation comprises an orientation for at least one of positive andnegative electrical connections for the LED package.
 3. The LED packageof claim 2, wherein the at least one symbol comprises at least one of aplus sign and a minus sign.
 4. The LED package of claim 2, wherein theat least one symbol comprises a plus sign and a minus sign.
 5. The LEDpackage of claim 1, wherein a gap is formed between the first contactpad and the second contact pad on the first side of the submount, and aportion of the solder mask is arranged in the gap.
 6. The LED package ofclaim 1, wherein the solder mask forms a first opening and the LED ismounted within the first opening.
 7. The LED package of claim 6, whereinthe solder mask forms a second opening over at least one of the firstcontact pad and the second contact pad.
 8. The LED package of claim 1,wherein at least one of the first contact pad and the second contact padforms at least one solder dam that is adjacent to the LED.
 9. The LEDpackage of claim 1, further comprising a lens that is molded over theLED and the submount.
 10. The LED package of claim 9, wherein the lenscomprises silicone with a Shore durometer of at least A70.
 11. The LEDpackage of claim 9, further comprising a protective layer that extendsfrom the lens to a side edge of the submount.
 12. The LED package ofclaim 11, wherein: the solder mask forms a first opening where the LEDis mounted; the solder mask forms a second opening over at least one ofthe first contact pad and the second contact pad; and a portion of theprotective layer extends over the second opening.
 13. The LED package ofclaim 1, wherein at least one of the first contact pad and the secondcontact pad comprises a die attach pad with a curved shape that radiallyextends toward one or more edges of the submount.
 14. The LED package ofclaim 13, further comprising a lens with a hemispheric shape, whereinthe lens is positioned over the die attach pad.
 15. A light emittingdiode (LED) package, comprising: a submount comprising a first side, asecond side that is opposite the first side, and a plurality of submountedges that are between the first side and the second side; a firstcontact pad and a second contact pad on the first side of the submount,wherein a gap is formed between the first contact pad and the secondcontact pad; an LED mounted on at least one of the first contact pad andthe second contact pad; a lens on the first side of the submount andover the LED; and a protective layer that extends between the lens andthe plurality of submount edges, wherein a portion of the protectivelayer covers the gap.
 16. The LED package of claim 15, wherein the firstcontact pad and the second contact pad cover at least 70% of the firstside of the submount.
 17. The LED package of claim 15, wherein the firstcontact pad and the second contact pad cover at least 75% of the firstside of the submount.
 18. The LED package of claim 15, wherein theprotective layer is arranged on at least a portion of the first contactpad and the second contact pad.
 19. The LED package of claim 15, whereina dimension of the first side of the submount is less than or equal to3.5 mm.
 20. The LED package of claim 15, wherein the submount comprisesone or more of aluminum oxide, aluminum nitride, polyimide, andpolyphthalamide.
 21. The LED package of claim 15, wherein the lenscomprises a molded lens over the LED and the submount.
 22. The LEDpackage of claim 21, wherein the lens comprises silicone with a Shoredurometer of at least A70.